class Solution {

public int myAtoi(String str) {

if (str == null || str.length() == 0 || str.trim().length() == 0) return 0;

String s = str.trim();

int i = 0, n = s.length(), maxIntLen = String.valueOf(Integer.MAX_VALUE).length();

char operator = ' ';

// step1: parse operator

if (i < n && (s.charAt(i) == '+' || s.charAt(i) == '-')) operator = s.charAt(i++);

// step2: parse zero

while (i < n && s.charAt(i) == '0') i++; // parse 0

// step3: get number string

StringBuffer sb = getNumStr(s, i);

// validation1: max length over max integer length

if (sb.length() > maxIntLen) return operator == '-' ? Integer.MIN_VALUE : Integer.MAX_VALUE;

// validateion2: exceed min/max value

long num = Long.parseLong(sb.toString()) * (operator == '-' ? -1 : 1);

if (num > Integer.MAX_VALUE) return Integer.MAX_VALUE;

if (num < Integer.MIN_VALUE) return Integer.MIN_VALUE;

return (int) num;

}

private boolean isDigit(char c) {

return c >= '0' && c <= '9';

}

private StringBuffer getNumStr(String s, int i) {

StringBuffer sb = new StringBuffer();

if (i >= s.length() || !isDigit(s.charAt(i))) {

sb.append(0); // leading char validation, return 0 if invalid

return sb;

}

while (i < s.length()) {

char c = s.charAt(i++);

if (!isDigit(c)) break;

sb.append(c);

}

return sb;

}

}